In most jurisdictions across North America laws have been enacted making it mandatory for a motor vehicle to be equipped with rear brake lights connected to a pedal activated brake. The brake lights are illuminated upon activation of the pedal activated brake. When one motor vehicle is following another, the illumination of the lights of the lead vehicle provides a driver of the following motor vehicle with warning that the lead vehicle is about to stop.
Most large trucks have an auxiliary braking system known as an "engine brake". The engine brake uses the engine to slow the vehicle down. The driver does not need to activate the pedal activated brake in order to activate the engine brake. As a consequence, the brake lights are not illuminated.
Every year accidents occur in which motor vehicles drive into the rear end of trucks that have slowed down using their engine brake.